Tellurium dioxide

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

The repeated (oral) dose studies (OECD 421 – highest dose 600 mg/kg/day) and OECD 408 (+ sperm analysis; highest dose 100 mg/kg/day), did not reveal indications that tellurium dioxide had adverse effects at any of the reproductive organs. 

In the OECD 421 study the NOAEL was 25 mg/ kg /day for the parental and fertility endparamaters.  

Link to relevant study records

Reference

Endpoint:

screening for reproductive / developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2012-10-16 to 2012-11-29 (in-life phase)

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 421 (Reproduction / Developmental Toxicity Screening Test)

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Research Models and Services, Germany GmbH, Sandhofer Weg 7, D-97633, from SPF colony
- Age at study initiation: Young adult rats, approximately 10 weeks old at starting and 12 weeks at mating.
- Weight at study initiation: 331-371 g males and 195-247 g females
- Fasting period before study: no data
- Housing: Type II and III polypropylene/polycarbonate, Rodents were group-housed as practical, up to 4 animals of the same group per cage
- Diet (e.g. ad libitum): ssniff® SM R/M ad libitum
- Water (e.g. ad libitum): tap water from municipal supply ad libitum
- Acclimation period: 6 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21.0 -24.8°C
- Humidity (%): 32 - 61 %
- Air changes (per hr): 15-20 air exchanges/hour
- Photoperiod (hrs dark / hrs light): light 12 hours daily, from 6.00 a.m. to 6.00 p.m.

Route of administration:

oral: gavage

Vehicle:

other: 1% aqueous Methylcellulose

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:

VEHICLE
- Justification for use and choice of vehicle (if other than water): 1% aqueous Methylcellulose (abbreviation: 1% MC) was used as vehicle.
- Concentration in vehicle:
- Amount of vehicle (if gavage): 5 mL/kg bw
- Lot/batch no. (if required): O16147824 (Dow Chemicals)

Details on mating procedure:

Mating began 2 weeks after the initiation of treatment with one female and one male of the same dose group (1:1 mating) in a single cage. Females remained with the same male during the 14-days mating period or until the copulation occurred.

A vaginal smear was prepared daily for each female during the mating period and stained with 1% aqueous methylene blue solution. The smears were examined with a light microscope, the presence of vaginal plug or sperm in the vaginal smear was considered as evidence of copulation (Day 0 of pregnancy as defined by the relevant guidelines). Sperm positive females were caged individually. Mating pairs were clearly identified in the data, mating of siblings was avoided.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analysis of test item formulations for concentration and homogeneity was performed on 3 occasions, during the first and last weeks and approximately midway during the treatment, using a validated ICP method based on the tellurium content.

Duration of treatment / exposure:

Males were dosed for 28 days (14 days pre-mating and 14 days mating/post- mating), then they were euthanized and subjected to necropsy examination.
Females were dosed for 14 days pre-mating, for up to 14 days mating period, through gestation and up to and including the day before necropsy, 4 days post-partum dosing. The day of birth (viz. when parturition was complete) was defined as Day 0 post-partum.

Frequency of treatment:

7 days/week

Details on study schedule:

Females 4503 and 4512 showed on evidence of copulation (not-mated) and not-delivered females 4501, 4504 and 4510 were sacrificed 26 days after the last day of mating, as practical.

All F1 offspring were terminated on Day 4 post-partum.

Remarks:

Doses / Concentrations:
0 mg/kg bw/d
Basis:
actual ingested

Remarks:

Doses / Concentrations:
25 mg/kg bw/d
Basis:
actual ingested

Remarks:

Doses / Concentrations:
120 mg/kg bw/d
Basis:
actual ingested

Remarks:

Doses / Concentrations:
600 mg/kg bw/d
Basis:
actual ingested

No. of animals per sex per dose:

12 male and 12 female animals per dose group

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: The dose levels were selected at 25, 120 and 600 mg/kg bw/day at a constant dose volume of 5 mL/kg, based on available data and information from previous experimental work, including the results of a preliminary dose range finding study
- Rationale for animal assignment:
All parental (P) animals were sorted according to body weight by computer and divided to weight ranges. There were an equal number of animals from each weight group in each of the experimental groups assigned by randomisation to ensure that animals of all test groups were as nearly as practicable of a uniform weight.

Positive control:

No positive control

Parental animals: Observations and examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily (at the beginning and end of each day)
- Cage side observations: Parental animals were inspected for signs of morbidity and mortality

DETAILED CLINICAL OBSERVATIONS: Yes
- General clinical observations were made once a day, after treatment at approximately the same time as practical. Pertinent behavioural changes, signs of difficult or prolonged parturition and all signs of toxicity including mortality were monitored.
- More detailed examinations were made once before the first exposure (to allow for within-subject comparisons), and at least once a week thereafter.
Signs evaluated included monitoring of any changes in skin, fur, eyes, mucous membranes, occurrence of secretions and excretions, and autonomic activity (e.g. lacrimation, piloerection, pupil size, unusual respiratory pattern), changes in gait, posture and response to handling as well as the presence of clonic or tonic movements, stereotypies (e.g. excessive grooming, repetitive circling), difficult or prolonged parturition or bizarre behaviour (e.g. self-mutilation, walking backwards). Special attention was directed towards the observation of tremors, convulsions, salivation, diarrhoea, lethargy, sleep and coma.

BODY WEIGHT: Yes
- Time schedule for examinations: All adult animals were weighed on Day 0, afterwards at least weekly and at termination.
Parent females were weighed on gestation Days GD0, 7, 14 and 20 and on postpartal Days PPD0 (within 24 hours after parturition) and 4
(before termination). The females were additionally weighed on GD4, 10 and 17 in order to give accurate treatment volumes.

FOOD CONSUMPTION AND COMPOUND INTAKE: Yes
Animal food consumption was determined by re-weighing the non-consumed diet with a precision of 1 g on Day 7 then at least weekly

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No

OTHER: On gestation day GD13 the sperm positive females were examined for the presence of vaginal bleeding or “placental sign” (intrauterine extravasation of blood as an early sign of pregnancy in rat).

Oestrous cyclicity (parental animals):

Detailed histological examination of the ovaries covered the follicular, luteal, and interstitial compartments of the ovary, as well as the epithelial capsule and ovarian stroma.

Sperm parameters (parental animals):

Special attention was paid to evaluation of the stages of spermatogenesis in the male gonads and histopathology of interstitial testicular cell structure.

Litter observations:

Each litter was examined as soon as possible after delivery to establish the number and sex of pups, stillbirths, live births, runts (pups that are
significantly smaller than normal pups) and the presence of gross abnormalities. Live pups were counted, sexed, weighed individually within 24 hoursof parturition (on the first day after parturition was complete, i.e. Day 0 or 1 post-partum) and on Day 4 post partum.

Observations are reported individually for each adult and offspring. All the litters were checked and recorded daily for the number of viable and dead pups. The dead pups found were subjected to necropsy with macroscopic examination. All observed abnormalities were recorded and are reported.
Some of the pups that were found dead were cannibalised, thus, they were counted and sex determined (when it was possible) but were not further
examined macroscopically.

Postmortem examinations (parental animals):

SACRIFICE
- Male animals: All surviving animals after 28 days, (14 days pre-mating and 14 days mating/post- mating)
- Maternal animals: All surviving animals were sacrificed after 4 days post partum.
Females showed on evidence of copulation (not-mated) and not-delivered females were sacrificed 26 days after the last day of mating, as practical.

GROSS NECROPSY
Gross necropsy was performed on each animal irrespective of the date of death.
After exsanguination the external appearance was examined, cranium, thoracic and abdominal cavities were opened and the appearance of the tissues and organs was observed macroscopically. Any abnormality was recorded with details of the location, colour, shape and size, as appropriate.

HISTOPATHOLOGY / ORGAN WEIGHTS
Detailed histological examination was performed on the selected list of retained organs (brain, uterus, ovaries, vagina, testes, epididymides, prostate, seminal vesicles with coagulating glands, and pituitary) in the control and High dose groups, found dead animals and any macroscopic findings (abnormalities) observed.
Special attention was paid to the organs of the reproductive system. The number of implantation sites and of corpora lutea was recorded.

At the time of termination, body weight and weight of the following organs of all parental animals were determined:
- With a precision of 0.01 g: uterus (with and without cervix), vagina, testes, epididymides, prostate, seminal vesicles with coagulating glands, brain
- With a precision of 0.001 g: ovaries, pituitary

Paired organs were weighed individually; absolute organ weights were measured and are reported. Relative organ weights (to body and brain weight) were
calculated and are reported.
The weighed organs and all organs showing macroscopic lesions of all adult animals were preserved. Testes and epididymides were preserved in
Bouin’s solution, all other organs in 10% buffered formalin solution.

Postmortem examinations (offspring):

SACRIFICE/GROSS NECROPSY
Pups euthanized at PND 4 were carefully examined at least externally for gross abnormalities.

Statistics:

The statistical evaluation of appropriate data was performed with the statistical program package SPSS PC+4.0. The homogeneity of variance between groups was checked by Bartlett’s homogeneity of variance test. Where no significant heterogeneity was detected, a one-way analysis of variance (ANOVA) was carried out. If the obtained result was significant, Duncan Multiple Range test was used to access the significance of inter-group differences. Getting significant result at Bartlett’s test, the Kruskal-Wallis analysis of variance was used and the inter-group comparisons were performed using Mann-Whitney U-test. Chi2 test was performed if feasible.

Reproductive indices:

Calculation of Mating and Fertility Indice
- Male Mating Index: Number of males with confirmed mating/ Total Number of males cohabited x 100
- Female Mating Index: Number of sperm-positve females/ Total Number of females cohabited x 100
- Male Fertility Index: Number of males impregnating a female/ Total Number of males cohabited x 100
- Female Fertility Index: Number of pregnant females/ Number of sperm-positve females x 100
- Gestation Index: Number of females with live born pups/ Number of pregnant females x 100

Offspring viability indices:

Calculation of Pups’ Mortality and Sex Ratio Indices:
- Survival Index: Number of live pups (at designated time)/ Number of pups born x 100
- Pre-implantation mortality: (Number of Corpora lutea – Number of Implantations)/ Number of Corpora lutea x 100
- Intrauterine mortality: (Number of implantations – Number of liveborns)/ Number of implantations x 100
- Total mortality: Number of implantations/ (Number of implantation – Number of viable pups (d4)) x 100
- Sex ratio: (Number of pups examined – Number of males) / Number of pups examined x 100

Clinical signs:

effects observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Other effects:

not examined

Reproductive function: oestrous cycle:

effects observed, treatment-related

Reproductive function: sperm measures:

no effects observed

Reproductive performance:

effects observed, treatment-related

CLINICAL SIGNS AND MORTALITY (PARENTAL ANIMALS):
Five female animals were found dead in the High dose group between Days 14 and 45. In addition one female treated at 600 mg/kg/day was found dead on Day 27. The death of this animal was accidental (gavage accident proved at necropsy).

Dark faeces were noted in all males and pregnant females treated at a dose level of 120 and 600 mg/kg/day. Limited use of hind-limbs was
observed in one male animal treated with 120 mg/kg/day.
In the surviving non-pregnant females treated at 600 mg/kg/day, decreased activity, dark faeces, hunched back, salivation, lethargy, piloerection and red liquid from the vulva were noted. The decreased activity, hunched back, piloerection and dark faeces were seen in all these High dose females.
In found dead animals, treatment-related clinical signs were observed including decreased activity, dark faeces, liquid faeces, hunched back, laboured respiration, lethargy, piloerection and red liquid from the mouth and vulva. Dark faeces were seen in all these animals.
In addition, occasionally clinical observations were noted, which were regarded as incidental finding and considered unrelated to treatment, missing
right testes; broken left incisor, and missing fur in the chin area.
No clinical signs were observed in animals treated at 25 mg/kg/day or in the control group.


BODY WEIGHT AND FOOD CONSUMPTION (PARENTAL ANIMALS)
Reduced body weight or body weight gain was observed in both sexes at 120 and 600 mg/kg/day; in males the terminal body weights were about 7% and 14% lower than control, in females the day 14 body weights were about 5% and 11% below controls at 120 and 600 mg/kg/day respectively,
although the effect became more pronounced in pregnancy. Food intake values were reduced in line with the body weight effects.
The Low dose group mean weights were unaffected by treatment.

REPRODUCTIVE FUNCTION: ESTROUS CYCLE (PARENTAL ANIMALS)
Toxicological significance effects were observed on the duration of the mating period in High dose animals. Successful coitus (sperm positive vaginal smears and/or vaginal plugs) occurred within up to 5 days of pairing (cohabitation), with the exception of High dose females 4503 and 4512, which did not have a sperm positive vaginal smear during the 14 days mating period. In addition, one High dose female animal no 4509 was found dead on the days 13 of the mating period, without successful coitus. Almost only dioestrus picture characterized the oestrus cycle of these animals.

REPRODUCTIVE FUNCTION: SPERM MEASURES (PARENTAL ANIMALS)
Histopathological evaluation of the male gonads as well as testicular interstitial cell structure, the spermatogenic cells representing different phases of the development and differentiation of the spermatozoa were similar in Control and High Dose males. There was no meaningful difference between incidence and severity of microscopic changes in the reproductive organs in High Dose males compared to Control males. Testicular observations had unilateral distribution in High Dose males. The incidence and severity were without a relationship to treatment and considered to be in the range of common background.

REPRODUCTIVE PERFORMANCE (PARENTAL ANIMALS)
The mating indices were 100% in the control, Low dose and Mid dose groups and 73% in the High dose group, while fertility indices were 100% in control, in Low and in Mid dose groups and 63% in High dose animals (due to 3/11 non-pregnant females). Gestation index was 92% in the control group (due to one animal no 1507 with stillborns, variation considered incidental), 100% in low dose group, 67% in Mid dose group (due to 4/12 animals with stillborns) and 0% in the High dose group.

ORGAN WEIGHTS (PARENTAL ANIMALS)
Males:
When compared to controls, statistically lower seminal vesicles weights were noted when measured as absolute values, and when adjusted for brain weights, in the High dose male animals (p<0.05). However, there was no histological evidence for any effects on the male reproductive system. Other statistical difference in male organ weights were ascribed to a consequence of body weight differences.

Females
When compared to controls, significantly lower vagina mean absolute weight was noted, about 47% below control in the High dose females (p<0.01).
This effect is probably related to ovary atrophy, since vagina weight is sensitive to changes in ovarian hormone production. The vagina weights of individual rats at this dose group show there was no influence of pregnancy on vaginal weight. There were a number of other statistical differences in relative organ weights, but at 120 and 600 mg/kg/day, weights of females at termination were about 18 % and 30 % below control, so the relative organ weight statistical differences were largely a consequence of body weight effects.

GROSS PATHOLOGY (PARENTAL ANIMALS)
In the six found dead High dose female animals, test item-related macroscopic changes were found in the variety of organs including black/grey discoloration/focus of the adrenal gland, brain, stomach, small intestines, caecum, colon, rectum, thymus, kidney, mesenteric lymph node and uterus. Pale discoloration of the liver was seen in 2 females. The small thymus present in one female was also regarded as test item-related and corresponded with similar change in terminal females from the High dose group.
Test item-related macroscopic findings were observed at dose levels of 120 and 600 mg/kg bw/day.
Four (4/6) females from the High Dose group were non-pregnant. A decrease or no corpora lutea and no implantation sites were seen in these animals at necropsy.
Small thymus in 4/6 High dose females and pale discoloration of the liver in 2/12 Mid dose and 1/6 High dose female rats, were present. Numerous organs were black/grey discoloured including the adrenal gland, brain, stomach, small intestines, caecum, colon, rectum, thymus, kidney, mesenteric lymph node, testis, ovary and/or uterus.


HISTOPATHOLOGY (PARENTAL ANIMALS)
Found dead animals
There were test item-related effects in the ovary, uterus, vagina, liver, kidney, thymus, mesenteric lymph node, stomach and caecum in 5 found dead females. One female was not histopathologically examined due to cannibalization of internal organs.

Minimal to moderate atrophy of the ovary, uterus and/or vagina in 3/5 females, moderate vacuolation of corpora lutea in the right ovary in 1/5 female, mild blue/black diffuse pigment deposits of the right ovary in 1/5 animal, were seen. In the liver, moderate hepatocellular necrosis and/or moderate diffuse vacuolation were found in 2/5 female rats. Mild bilateral necrosis of cortical tubules in the kidney associated with mild mixed cellular peritubular/perivascular infiltrate and moderate lymphoid atrophy of the thymus altered were seen in 1/5 found dead rat. Minimal or moderate accumulation of pigmented macrophages in the medulla of the mesenteric lymph node was noted in 3/5 animals. Mild mucosal erosion of the glandular stomach in 1/5 female and mild granular/crystalline foreign material in the lumen of caecum in 1/5 female rat, were also evaluated.
Other changes were incidental or agonal in nature and not related to treatment.


Scheduled necropsy
Test item-related findings were observed by light microscopy. At a dose level of 600 mg/kg bw/day, these changes were noted in the ovary, vagina, uterus , liver and mesenteric lymph node. In the females dosed at 120 mg/kg bw/day, the liver was only organ which was affected. These changes were characterized as atrophy of the ovary, uterus, vagina and/or thymus, blue/black pigment deposits in the ovary, accumulation of pigmented macrophages in mesenteric lymph node and hepatocellular vacuolation or necrosis in the liver. In the ovary, reduced number/size of follicles/corpora lutea, were observed. Occasionally, blue/black diffuse pigment deposits were present in the ovary. Low columnar luminal and glandular epithelium, reduced endometrium/myometrium were seen in the uterus. Attenuated epithelium comprising 2-3 cell layers was noted in the vagina. Lymphoid atrophy of thymus was accompanied with decreasing number of lymphocytes leading to decreased cell density, decreased compartment size (more pronounced in cortex), which also corresponded with organ weight change related brain weight. In the mesenteric lymph node, various degree of pigmented macrophages in the medulla was described. Vacuolation of hepatocytes contained predominantly large well-defined round vacuoles, with displaced nucleus to the periphery was one of the microscopic feature in the liver. Nuclei underwent lysis and increased eosinophilia of the cytoplasm, were typical for necrotic process in the liver. Mixed cell infiltrate could be also seen.
There was a consistent relationship to dose in the severity and incidence of these test item-related microscopic effects.
In the males, dose-related accumulation of pigmented macrophages was microscopically observed at dose levels 120 and 600 mg/kg bw/day in the mesenteric lymph node and corresponded with changes noted at necropsy.

Dose descriptor:

NOAEL

Effect level:

600 mg/kg bw/day (actual dose received)

Based on:

act. ingr.

Sex:

male

Basis for effect level:

other: Reproductive toxicity There were no effects identified on the male reproductive system.

Dose descriptor:

NOAEL

Effect level:

25 mg/kg bw/day (actual dose received)

Based on:

act. ingr.

Sex:

female

Basis for effect level:

other: Reproductive toxicity in parental females at 120 and 600 mg/kg/day was not considered secondary to systemic toxicity.

Dose descriptor:

NOAEL

Effect level:

25 mg/kg bw/day (actual dose received)

Based on:

act. ingr.

Sex:

male/female

Basis for effect level:

other: NOAEL for systemic effects of parental generation

Clinical signs:

not examined

Mortality / viability:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Sexual maturation:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

effects observed, treatment-related

Histopathological findings:

not examined

VIABILITY (OFFSPRING)
There were no live born pups in the High dose group. From 19 examined pups, 16 pups were found dead and presented negative floating test and were not suckled and 3 were cannibalised on Day 0.
In the 120 mg/kg/day Mid dose group, 33/137 pups were possibly stillborn, 28/137 were found dead but born alive (presented positive floating test), 39 were cannibalized and 65 were not suckled. Of the pups which died PND0-PND4, there were more males than females.
In the Low dose, there was no effect on the number of live born pups (148/173). Lack of suckling was observed in 33 pups, one pup was pale and one was cold and cyanotic. The survival index of about 75% on PND4 is in below the normal control range.


CLINICAL SIGNS (OFFSPRING)
not examined

BODY WEIGHT (OFFSPRING)
Adverse effects considered related to Tellurium dioxide were observed with regard to offspring body weight on PND 0 in animals treated at 25, 120 and 600 mg/kg bw/day.
When compared to controls, the mean litter weights on PND 0, pups body weight evaluated on PND 0 for all pups or per litter, were lower in the F1 generation following administration of 25, 120 and 600 mg/kg/day daily by oral gavage, to the parental generation. These differences attained statistically significance in PND 0 body weight for all pup means (p<0.05 or p<0.01).
The pup body weight evaluated on PND 4 and the body weight gain was similar to the control in the Low and Mid dose animals. However, the total litter weights were considered to be below the normal control range in the Mid dose group on PND 0 and 4, and in the Low dose group at PND 0; these effects were ascribed to pup mortality rather than an effect on the weight of surviving pups.

The differences seen in the Low, Mid and High groups were considered to be a consequence of pup mortality, without an effect on the growth of survivors.

SEXUAL MATURATION (OFFSPRING)
not examined

ORGAN WEIGHTS (OFFSPRING)
not examined

GROSS PATHOLOGY (OFFSPRING)
Test item-related gross changes were observed in the cranium region and skin/subcutis in the High Dose group pups (two litters affected). In four found dead pups from the High Dose group, the absence of cranial region of the head with reduced brain size, covered by skin were noted. Whole body subcutaneous gelatinous material was recorded in 16 found dead pups.

HISTOPATHOLOGY (OFFSPRING)
not examined

OTHER FINDINGS (OFFSPRING)

Dose descriptor:

LOAEL

Generation:

F1

Effect level:

25 mg/kg bw/day (actual dose received)

Based on:

act. ingr.

Sex:

male/female

Basis for effect level:

other: pup mortality at 25 mg/kg/day

Reproductive effects observed:

not specified

No test item was identified in the control samples. The test item formulation appeared to be homogenous and had actual concentrations of 95.2-105.3% of the nominal concentrations, within the 100±15% acceptable range.

These results were considered suitable for the study purposes.

Conclusions:

The No Effect Level for effects on the Parental generation was considered to be 25 mg/kg/day.
There was no No Effect Level for reproductive effects, due to pup mortality at 25 mg/kg/day.
There were no effects identified on the male reproductive system.

Executive summary:

In a screening study according to OECD guideline 421 Tellurium dioxide was administered by repeated oral gavage daily administration to Wistar rats at 0, 25, 120 and 600 mg/kg bw/day in 1% aqueous Methylcellulose. Males were dosed for 28 days (14 days pre-mating and 14 days mating/post- mating) and females were dosed for 14 days pre-mating, for up to 14 days mating period, through gestation and up to and including the day before necropsy, 4 days post-partum dosing.

 

At 600 mg/kg/day treatment related effects in females included mortality (5/12), clinical signs of decreased activity, hunched back, piloerection and dark faeces. In males and females at 120 and 600 mg/kg/day dark faeces was observed.

Reduced body weight or body weight gain was observed in both sexes at 120 and 600 mg/kg/day; in males the terminal body weights were about 7% and 14% lower than control, in females the day 14 body weights were about 5% and 11% below controls at 120 and 600 mg/kg/day respectively, although the effect became more pronounced in pregnancy. Food intake values were reduced in line with the body weight effects. The Low dose group mean weights were unaffected by treatment.

At 600 mg/kg/day there were adverse effects of treatment on the oestrus cycle, mating ability, fertility and gestation period. At 120 mg/kg/day the gestation period was prolonged. Higher intrauterine mortality, post-natal or total mortality were recorded at 120 and 600 mg/kg/day. Also at the Low dose, post-natal and total mortality was considered to be increased. There were no surviving pups at 600 mg/kg/day. Mortality data indicate a higher mortality in male pups than female pups in the 120 mg/kg/day group.

Examination of pups at 600 mg/kg/day, all were found dead, showed evidence of foetotoxic effects and possibly a developmental effect of the test item particularly on the cranial and brain development. The cause of death in pups at 25 and 120 mg/kg/day was not evident.

There were no evident effects on pup weight or weight gain in the surviving pups. Total litter weights at termination were reduced at 120 mg/kg/day this was considered to be a consequence of pup mortality.

At necropsy and histopathology, at 600 mg/kg/day there was a test item related atrophy of female reproductive tissues, which could account for the lack of mating and adverse embryo and foetal effects, with likely endocrine effects related to ovarian atrophy. There were signs of intestinal, hepatic and mesenteric lymph node toxicity, with some effects in kidney and thymus, there were pigment deposits in a number of affected tissues. The reproductive organ effects in females are not considered to be secondary effects of systemic toxicity. At 120 mg/kg/day females showed signs of hepatotoxicity but no apparent effects on reproductive organs. There were no effects identified on the male reproductive system.

 

The No Effect Level for effects on the Parental generation was considered to be 25 mg/kg/day.

There was no No Effect Level for reproductive effects, due to pup mortality at 25 mg/kg/day. Reproductive toxicity in parental females at 120 and 600 mg/kg/day was not considered secondary to systemic toxicity.

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

25 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Effects on developmental toxicity

Link to relevant study records

Reference

Reference 1

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Principles of method if other than guideline:

Developmental toxicity study, rats were exposed subcoutaneous from day 15 to 19 of gestation.

GLP compliance:

not specified

Limit test:

no

Species:

rat

Strain:

Wistar

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Biological Laboratories, Wilmengotn, MA
- Age at study initiation: no data
- Weight at study initiation: 170 – 200 g
- Fasting period before study: no data
- Housing: Dams recognized as pregnant were housed individually in standard plastic cages on Pine-Dri shavings.
- Diet (e.g. ad libitum): Purina Chow 5001 ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: no data

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 °C
- Humidity (%): 40 -50 %
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12 hour dark/light cycle

Route of administration:

subcutaneous

Vehicle:

olive oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
Tellurium dioxide was suspended in olive oil given as 1 mL/kg maternal body weight

Details on mating procedure:

Rats were bred by individual housing with a male overnight.
Day zero for pregnancy was determined by the presence of sperm plugs in cage debris.

Duration of treatment / exposure:

females: day 15 to 19 of gestation

Frequency of treatment:

females daily from day 15 to 19 of gestation

Duration of test:

At day 20 dams were euthanatized by ether

No. of animals per sex per dose:

10 dams per group

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: No details reported; previously published information was taken into account.

Maternal examinations:

Maternal toxicity was evaluated by using the following parameters: maternal lethality, gross morphological changes, body weight changes during the period of exposure and histological evaluation of kidney and liver at day 20 of gestation.

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: Yes
- Number of corpora lutea: no
- Number of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: Yes
- Other:

Fetal examinations:

The viability of the fetuses was determined by the presence of spontaneous breathing or response to a tactile stimulus.

Live fetuses were killed by CO2 and assigned for soft-tissue examination; half were scheduled for fresh internal exam and the other half for the Wilson section technique (Wilson, ´64). All dead pups were analyzed via the Wilson technique.

- External examinations: Yes: all per litter
- Soft tissue examinations: Yes: half per litter
- Skeletal examinations: Yes: half per litter
- Head examinations: Yes: 2 per litter

Statistics:

The litter was used as the experimental unit. Normality test was performed by the Kolmogorov – Smirnov test (Massey, ´51). Comparison of normally distributed groups of parametric data was performed by one-way analysis of variance (ANOVA) (Armitage, ´71). A significant F value in the ANOVA was followed by the unpaired Student´s t-test to establish which groups differ significantly from controls.

Historical control data:

no information

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
In this study, doses of 500 and 1000 µmol /kg of TeO2 were maternally toxic. This toxicity was expressed as weight loss, centrolobular fatty change in the liver, and as a 40% lethally (4/10) at the highest dose. Neither maternal weight loss nor liver changes were found in the 10 and 100µmol/kg group.

Dose descriptor:

NOAEL

Effect level:

100 other: µmol/kg bw/d Tellurium as Tellurium dioxide

Based on:

act. ingr.

Basis for effect level:

other: maternal toxicity

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:yes

Details on embryotoxic / teratogenic effects:
At 500 and 100 µmol/kg 11 and 81 % fetal mortality rates were recorded. No fetal mortality was observed in the other exposure groups.
A dose-related decrease in fetal weight was observed.
A dose-related decrease in fetal size was observed. This decrease was particularly evident when body length was compared among groups. A significant increase in the measurements at the level of the neck was observed at doses of 100 and 500 µmol/kg. This increase in diameter could be explained ba the presence of soft tissue with many skin folds which are very easily distensible; thus edema could be documented.

The presence of abnormal accumulation of fluid in the subcutis was recorded as edema during the external examination. This process of fluid accumulation, which produced a subsequent distention of the sin and generalized deformity, was corroborated after fixation of the fetuses in Bouin´s solution.

Edema was externally evident in fetuses posed to TeO2 at doses ≥ 100 µmol/kg and the severity of this process was dose-related. No edema was observed at 10 µmol/kg dose or in the control groups.
Fetuses with dilation of the cerebral ventricles were considered hydrocephalic. The hydrocephalus in all cases was defined as communicating. This hydrocephalus was observed to be expansion of all cavities in the CSF pathways and no obstruction within the brain itself as determined in sagittal section of brains. There was 100 % incidence of this phenomenon in animals exposed to doses ≥ 100 µmol/kg. different degrees of hydrocephalus were noted, from moderate ventricular dilation with a thick cortical area at 100mmol/kg level, to severe cases at 500 and 1000 µmol/kg dose, where the cortex was reduced to a very thin layer. This severity was dose related. Hydrocephalus was not observed upon fetal examination at the 10 µmol/kg dose or in the controls.
Open eyes were noted in fetuses exposed to TeO2 at dosed ≥ 500 µmol/kg. Cases in which the eye was externally protruded were classified as exophthalmia. Ocular hemorrhage was also present in fetuses exposed to 100 µmol/kg where no open eyes were observed. None of these abnormalities was observed at the 10 µmol/kg level and controls.

Internal examination of the pelvis revealed the presence of small kidneys and undescended testis in day 20 fetuses. Both of these effects were dose related. The presence of intestine in the umbilical cord and subsequent distension of this structure were recorded as umbilical hernia. This herniation was present in some fetuses exposed to ≥ 500 µmol/kg.

Skeletal analysis was unremarkable.

Dose descriptor:

NOAEL

Effect level:

10 other: µmol/kg bw/d Tellurium as Tellurium dioxide

Based on:

act. ingr.

Basis for effect level:

other: The most prominent effects were observation of hydrocephalus followed by increase in fetal mortality at higher doses.

Abnormalities:

not specified

Developmental effects observed:

not specified

Conclusions:

NOAEL (F1 generation) for developmental toxicity for male/female off-spring: NOAEL 10 µMol/kg bw/d as Tellurium dioxide
The most prominent effects were observation of hydrocephalus followed by increase in fetal mortality at higher doses.
The adverse effects on the fetuses were also observed without evidence of maternal toxicity.

Executive summary:

The following information was considered relevant and is cited from the publication:

"The effects of multiple maternal subcutaneous injections of Tellurium dioxide (TeO2) suspended in olive oil (0-1,000 μMol/kg) from day 15 to day 19 of gestation were evaluated in the Wistar rat.

External and internal soft-tissue examinations were performed on day 20 fetuses. Multiple maternal injections, at doses higher than 10 μMol/kg, resulted in a dose-related appearance of hydrocephalus, edema, exophthalmia, ocular hemorrhage, umbilical hernia, undescended testis, and small kidneys in fetuses on day 20 of gestation.

 

At 500 μMol/kg, reduction in maternal weight gain was also observed. At this level, the incidence of the above anomalies was 100 %. The 100 μMol/kg dose of Tellurium, which did not produce apparent maternal toxic responses, resulted in a 100 % incidence of hydrocephalus and edema but no fetal mortality. Thus, Tellurium can be teratogenic to the rat fetus without concomitant maternal toxicity.

Also, the fetal period may be more sensitive than the organogenic period for the induction of hydrocephalus. Such evidence is consistent with the development of the choroid plexus and an effect of TeO2 on the production/resorption of cerebrospinal fluid."

Reference 2

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Acceptable, well-documented publication, which meets basic scientific principles

GLP compliance:

not specified

Species:

rat

Strain:

Wistar

Route of administration:

subcutaneous

Vehicle:

olive oil

Duration of treatment / exposure:

females: day 15 to 19 of gestation

Frequency of treatment:

females: daily from day 15 to 19 of gestation

No. of animals per sex per dose:

5 per dose group

Details on study design:

In the pair-fed study food consumption was measured in the tellurium-treated rat and the same quantity of food was given to a second rat that was bred one day later and then received vehicle alone.

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
Reduction in body weight

Dose descriptor:

conc. level:

Effect level:

500 other: µmol/kg bw

Based on:

test mat.

Basis for effect level:

other: developmental toxicity

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:yes

Details on embryotoxic / teratogenic effects:
100 % incidence of hydrocephalus was the most prominent finding

Abnormalities:

not specified

Developmental effects observed:

not specified

The significant reduction in maternal weight gain, observed in the tellurium exposed dams, can be attributed to a reduction in food consumption, since a similar response was observed in the pair –fed controls. 

In rats treated with 500μmol/kg Tellurium dioxide, a 100 % of incidence of hydrocephalus, edema, exophthalmia, ocular hemorrhage, umbilical hernia, undescended testes and small kidneys was observed in all exposed litters, but none of these abnormalities was observed in fetuses from dams fed ad libitum or in the pair-fed controls.

In some instances, maternal food restriction may be directly related to birth defects in animal models. For TeO2, it is apparent that acute maternal dietary alterations are not the primary factors in the production of the anomalies noted.

Conclusions:

TeO2 can produce maternal toxicity and teratogenicity.
However, the reduction in food intake is untrelated to the teratogenic response to Tellurium in the rat.

Executive summary:

The following information was considered relevant and is cited from the publication:

"Tellurium dioxide induced hydrocephalus, edema, exophthalmia, ocular hemorrhage, umbilical hernia, undescended testes and small kidneys in day 20 Wistar rat fetuses when administered s.c. to pregnant dams from gestational day 15 to 19. At doses of 500μmol/kg or greater, a 100% incidence of these findings and a reduction of maternal weight gain were observed. A pair-fed study at the dose of 500μmol/kg of TeO2 was conducted to establish if the effects of tellurium were a result of a reduction in food intake or other maternal toxic response. Two additional groups of rats receiving tellurium or vehicle were fed ad libitum. After a comparable maternal weight gain from day 0 to 15, weight gain was significantly reduced in the treated groups and the pair-fed control. There was a reduction of fetal weight in the trated groups (p < 0.01) and in the pair-fed control (p < 0.02). There was a 100 % incidence of the above anomalies in the litters for the two treated groups, but none in the pair-fed and control groups. No histological alterations other than a mild centrolobular fatty change in the liver were detected in the other organs from the tellurium exposed dams. Thus, tellurium induced both maternal toxicity and teratogenic effects in the rat where the teratogenicity is not mediated by alterations in the diet."

Reference 3

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: not a relevant standard method

Species:

rat

Route of administration:

intramuscular

Dose descriptor:

dose level:

Effect level:

13 mg/kg bw/day

Based on:

test mat.

Basis for effect level:

other: developmental toxicity

Abnormalities:

not specified

Developmental effects observed:

not specified

Conclusions:

The precise period of teratogenic susceptibility of the rat embryo to Tellurium was investigated.

Executive summary:

The precise period of teratogenic susceptibility of the rat embryo to Tellurium was investigated by limiting the maternal administration of the metal to single injections on specific days of gestation. 13 mg/kg body weight was administered by i.m. injection to 5 to 10 pregnant rats for each day 7 to 13 of gestation. The dams were allowed to deliver and the offspring was observed closely for 10 postnatal days. After sacrifice the pubs were examined for hydrocephalus and other defects. Mothers failing to deliver were autopsied and examined for fetal resorption sites the day following the predicted delivery. The embryonic period of teratogenic susceptibility to Tellurium falls onto the days 9 and 10 of gestation with an incidence of 18.6 and 31.0 % hydrocephalus, respectively. Malformations other than hydrocephalus were not observed.

Additional information

In the following four key studies will be first comprehensively described by their decisive study parameters and from the summarized results basic conclusions will be drawn with regard to the interpretation of elemental Tellurium`s reproductive/developmental potency and derived effect levels thereof (taking also into account the subacute repeated dose toxicity study).

Several studies on toxicity to reproduction are available for elemental Tellurium and Tellurium dioxide as has been shortly outlined in the literature searches attached in Section 12 of the registration dossier.

 

Duckett and coworkers evaluated the pathological mechanisms and morphology of Tellurium induced hydrocephalus in rats at doses of 2500 and 3000 ppm, which are fare above the derived effect levels in the selected key studies.

 

Garroet al.described a dose depending development of hydrocephalus at doses between 500 and 2500 ppm Tellurium in the diet, with special attention on the pathogenesis of hydrocephalus.

 

Agnew and coworkers investigated the precise period of teratogenic susceptibility of the rat embryo by single injections of 13 mg/kg body weight on specific days of gestation.

 

Perez-D´Gregorio evaluated the influence of a decrease in maternal body weight on teratogenic effects in a pair–feed study and showed that teratogenicity is not mediated by alterations in the diet.

 

However, most of the reported studies were not conducted according to an internationally accepted test guideline nor any standard procedures. Furthermore the target of the investigations was outside the scope of the assessment necessary under the REACH Regulation.

 

Despite the mentioned restrictions and the focus put onto (only) four key studies, it can be stated that considering the dose response relationship and the observed effects a consistent picture can be drawn from the available data base.

 

Key Studies for the endpoint reproductive/developmental toxicity

For the determination of equitoxic potency of various Tellurium moieties (in this case elemental Tellurium and Tellurium dioxide) and hence definition of the NOAEL and furtheron derivation of DNELs the relative bioavailability is the most important figure.

 

Bioavailability

For this purpose in vitro studies with elemental Tellurium (Te) and Tellurium dioxide (TeO₂) were conducted to assess their behavior in a physiological environment with regard to any toxicokinetic differences.

Therefore bioavailability simulating inhalation and oral uptake was measured by the substance`s solubility in artificial alveolar fluid and in artificial saliva and gastrointestinal fluid respectively.

 

The results indicate that Tellurium dioxide is of approximately three times higher solubility than elemental Tellurium (see following table for measured solubility data):

 

	Tellurium [mg/L]	Tellurium dioxide [mg/L]
Mean solubility in artificial alveolar fluid after 72 hours	238.4 ± 16.1	799.1 ± 7.3 (Te) 999.4 ± 9.1 (Tellurium dioxide)
Factor	3.35 (based on Te)
Mean solubility in artificial gastrointestinal fluid	56.68 ± 1.46	156.7 ± 13.2 (Te) 196.03 ± 16.5 (Tellurium dioxide)
Factor	2.76 (based on Te)

 

It is a well-accepted fact, that such in vitro studies with inorganic substances may underestimate the in vivo bioavailability, because living cells do possess active transport systems to control for homeostatic reasons the uptake of for example essential elements. Nevertheless the in vitro data does allow for a comparative insight into the bioavailability of different redox-species of an element and are therefore suitable for comparing study results with different Tellurium compounds in particular since the element Tellurium is not thought to be essential.

Despite total lack of information, the relative absorption after dermal exposure compared with oral exposure may be estimated by using data from other metals:

The Health Risk Assessment Guidance for Metals (HERAG) proposes for dermal absorption after exposure to dust or other dry metal compounds a default value of 0.1 % [11].

From this it follows that the dermal systemic bioavailability of elemental Tellurium may be estimated to be 10 % of the oral bioavailability (based on 10 % oral uptake) which results in a systemic bioavailability of 1 % of the external dermal dose. This figure clearly exceeds the above mentioned 0.1 % as typical for other metals and can therefore be considered a very conservative approach.

The figure of 1 % of dermal uptake of Tellurium will be used further in the exposure considerations

 

Tellurium dioxide: Reproductive/developmental toxicity screening test following oral (gavage) administration in Wistar rats

 

Technical description of the study:

• Test substance: Tellurium dioxide


• Method: OECD Guideline 421 (Reproductive/Developmental Toxicity Screening Test)


• Species: male/female rat (Wistar)


• Type of study: screening reproductive/developmental toxicity study


• Route: oral gavage


• Experimental animals: 12 rats per sex/group


• Dosing period for males: 28 days (14 days pre-mating and 14 days mating/post mating)


• Dosing period for females: 14 days pre-mating, up to 14 days mating, through gestation and 4 days post-partum dosing. 


• Dosing for males and females:0, 25, 120 and 600 mg/kg body weight (bw) per day (d) [mg/kg/d]

 

Study results: 

• NOAEL (parenteral generation) for reproductive toxicity to males: 600 mg/kg bw/d (highest dose applied)

There were no effects identified on the male reproductive system.

 

• NOAEL (parenteral generation) for reproductive toxicity to females: 25 mg/kg bw/d.

Effects observed at 120 and 600 mg/kg/d are not considered secondary to systemic toxicity. At 600 mg/kg/d there were adverse effects of treatment on the oestrus cycle, mating ability, fertility and gestation period. Similar but lesser effects were seen at 120 mg/kg/d. Higher intrauterine mortality, post-natal and/or total mortality were recorded at 120 and 600 mg/kg/d.

 

• NOAEL (parenteral generation) for systemic effects: 25 mg/kg bw/d

At 600 mg/kg/d treatment related effects in females included mortality (5/12), clinical signs of decreased activity, hunched back, piloerection and dark feces. In males and females at 120 and 600 mg/kg/d dark feces were observed.

 

Reduced body weight or body weight gain was observed in both sexes at 120 and 600 mg/kg/d; in males the terminal body weights were about 7 % and 14 % lower than control, in females at day 14 body weights were about 5 % and 11 % below controls at 120 and 600 mg/kg/d respectively, although the effect became more pronounced in pregnancy.

 

• NOAEL (F1 generation) for male/female offspring: No NOAEL identified,because pup mortality was also observed in the low dose group at 25 mg/kg/d.

 

Interpretation of study results with respect to toxicity profile of Tellurium dioxide:

No NOAEL could be identifiedwith respect to reproductive/developmental toxicity, because also in the lowest dose group of 25 mg Tellurium dioxide/kg body weight per day severe effects (i.e. dead of pups) were observed.

The adverse effects on the off-spring were also observed without maternal toxicity because the NOAEL for reproductive toxicity to females was 25 mg/kg body weight per day.

 

The study did not show any specific target organ toxicity of Tellurium.

Males were unaffected by administration of Tellurium dioxide with regard to reproductive toxicity.

 

Perez-D’Gregorio et al.: Teratogenicity of Tellurium dioxide: prenatal assessment

 

Technical description of the study:

 ·      Test substance: Tellurium dioxide

·      Species: female rat (Wistar)

·      Type of study: developmental toxicity study

·      Route: multiple maternal subcutaneous injections

·      Experimental animals: 10 dams per group

·      Exposure: females for gestational days 15 to 19

·      Dosing: 0, 10, 100, 500 and 1000 µMol Tellurium/kgas Tellurium dioxide

·      Observations: examination of fetuses on day 20

 

Study results: 

• NOAEL (parenteral generation) for maternal toxicity: 100 µMol/kg bw/d

Toxicity was expressed as weight loss, centrolobular fatty change in the liver and 40 % lethality at the highest dose

 

• NOAEL (F1 generation) for developmental toxicity for male/female off-spring: NOAEL 10 µMol/kg bw/d as Tellurium dioxide

The most prominent effects were observation of hydrocephalus followed by increase in fetal mortality at higher doses.

 

·      At 500 and 1000 µMol/kg bw/d 11 % and 81 % mortality were recorded for day 20 fetuses. 100 % incidence of hydrocephalus was noted at doses of ≥ 100 µMol/kg bw/d with a dose related increase in severity.

 

 

Explanation of dose for route to route extrapolation:

 

·      Factor for route to route extrapolation subcutaneous -> oral: 2 as a very conservative approach

 

·      10 µMol Tellurium dioxide/kg/dareequivalent to 1596.1 µg Tellurium dioxide/kg/d

 

·      Additional application of a factor of 2 for route to route extrapolation gives the following values:

 

-    10 µMol TeO₂/kg/dsubcutaneously =    3.19 mg Te O₂/kg/d orally

-  100 µMol TeO₂/kg/dsubcutaneously =    31.9 mg Te O₂/kg/d orally

-  500 µMol TeO2/kg/d subcutaneously = 159.5 mg Te O₂/kg/d orally

- 1000 µMol TeO2/kg/d subcutaneously =    319 mg Te O₂/kg/d orally

 

Interpretation of study results with respect to toxicity profile of Tellurium dioxide:

From the subcutaneous NOAEL of 10 µMol Tellurium dioxide/kg body weight per day fordevelopmental toxicity of male/female F1 generation an equivalent oral NOAEL of 3.19 mg Tellurium dioxide/kg body weight per day follows with regard to development of hydrocephali.

The adverse effects on the fetuses were also observed without evidence of maternal toxicity.

 

E. M. Johnson et al.: Developmental investigation of Tellurium, study on rats

 

Technical description of the study:

·      Test substance: Tellurium

·      Species: female rat (Sprague-Dawley)

·      Type of study: developmental toxicity study

·      Route: oral feeding study

·      Experimental animals: 32 to 33 dams per group

·      Exposure: females for gestational days 6 to 15

·      Dosing: 0, 30, 300, 3000 and 15000 ppm Tellurium in diet

·      Observations: examinations of 2/3 of fetuses of test groups on day 20; 1/3 of the rats were permitted to deliver naturally and off-spring was observed for 7 days.

 

Study results:

·      The test substance was added to foodstuff, the fact of which may lead to a lower bioavailability because adsorption of Tellurium to foodstuff may be likely.

 

·      Also for the control group one hydrocephalus was reported.

 

• NOAEL (parenteral generation) for maternal toxicity: 30 ppm

Maternal toxicity was evident by decreased feed consumption and decreased body weight gain in groups receiving ≥ 300 ppm Tellurium in the diet.

 

• NOAEL (F1 generation) for male/female off-spring: 300 ppm Tellurium in the diet

Both skeletal and soft tissue malformations, primarily hydrocephali were noted in the off-spring of rats exposed to 3000 and 15000 ppm Tellurium in diet.

 

Explanation of conversion of dose for elemental Tellurium into equivalent dose for Tellurium dioxide:

Conversion of amount of elemental Tellurium in the diet to dose in mg per kg body weight and day has been done by E. M. Johnsonet al. and is reproduced in the following:

 

-      30 ppm Tellurium in the diet =     2.2 mg Te/kg/d

-    300 ppm Tellurium in the diet =   19.6 mg Te/kg/d

-  3000 ppm Tellurium in the diet = 165.6 mg Te/kg/d

- 15000 ppm Tellurium in the diet = 633.4 mg Te/kg/d

 

Test substance: Tellurium

 - Factor for higher bioavailability of TeO₂compared to Te: 3:

- 19.6 mg elemental Te are (biologically) equivalent to 6.53 mg Te in TeO₂due to threefold higher bioavailability of Tellurium dioxide

  - Atomic weight for Te: 127.61 g/Atom; molecular weight for TeO₂: 159.61 g/Mol, i.e. resulting in a conversion factor of 1/1.251 = 0.799: i.e. 6.53 mg Te in TeO₂are equivalent to approximately 8.2 mg TeO₂, therefore:

 

 

-      30 ppm Tellurium in the diet =     2.2 mg Te/kg/d =   0.92 mg TeO₂/kg/d 

-    300 ppm Tellurium in the diet =   19.6 mg Te/kg/d =     8.2 mg TeO₂/kg/d 

-  3000 ppm Tellurium in the diet = 165.6 mg Te/kg/d =   69.1 mg TeO₂/kg/d 

- 15000 ppm Tellurium in the diet = 633.4 mg Te/kg/d = 264.2 mg TeO₂/kg/d 

 

 

Interpretation of study with respect to toxicity profile of Tellurium dioxide:

 

From this study a NOAEL of 8.2 mg/kg/d for Tellurium dioxide can be derived with respect to reproductive/developmental toxicity.

 

The maternal NOAEL for systemic toxicity is 0.92 mg Tellurium dioxide/kg body weight per day but it is to be noted that the observed “toxicity” at the next higher dose of 8.2 mg Tellurium dioxide /kg body weight per day is very unspecific because only decreased feed consumption and decreased body weight gain was observed.

 

In light of the fact that formation of hydrocephalus, i.e. a very severe and specific effect, occurred already at this dose clearly indicates that the observed developmental toxicity is unrelated to the slight onset of unspecific maternal toxicity.

 

E. M. Johnson et al.: Developmental investigation of Tellurium, study on rabbits

 

This study forms part of the publication of E. M. Johnson et al..

 

Since rabbits which have been used instead of rats may be less sensitive compared to the rat (less severe effects were observed), this study is used as a more supporting study for classification purposes, but not for DNEL derivation.

 

Technical description of the study:

·      Test substance: Tellurium

·      Species: female rabbit (New Zeeland white)

·      Type of study. developmental toxicity study

·      Route: oral feeding study

·      Experimental animals:17 dams per group (artificially inseminated)

·      Exposure: females for gestational days 6 to 18

·      Dosing: 0, 125, 175, 1750 and 5250 ppm Tellurium in the diet

·      Observations: on day 29 of presumed gestation, all surviving does were killed.

 

Study results: 

• NOAEL (parenteral generation) for maternal toxicity: 175 ppm Maternal toxicity was evident by decreased feed consumption and decreased body weight gain in groups receiving ≥ 1750 ppm Tellurium in diet.

 

• NOAEL (F1 generation) for male/female off-spring: 300 ppm Rabbit fetuses of the highest dose group had slightly elevated evidence of skeletal delays and nonspecific abnormalities.

 

Interpretation of study results with respect to toxicity profile of Tellurium dioxide:

 

From this study an oral NOAEL on rabbits of 300 ppm equivalent to12 mg Tellurium/kg body weight per daycan be derived with respect to reproductive/developmental toxicity.

Explanation and conversion of dose for elemental Tellurium into equivalent dose for Tellurium dioxide (as outlined for the study with rats) will result in an oral NOAEL on rabbits of 5 mgTellurium dioxide/kg body weight per day.

 

Even though effects in fetuses were less severe than in rat fetuses adverse effects were clearly observed at a dose which did not lead to overt maternal toxicity.

 

 

Summary of observed effects with regard to reproductive/developmental toxicity

 

It should be noted that no study exists which specifically covers reproductive toxicity with regard to sexual function and fertility.  However information can be deduced from the OECD 421 screening study and in the subacute repeated dose toxicity study (OECD 408) described above.   

In the screening study with Tellurium dioxide at 600 mg/kg body weight per day there were adverse effects of treated females on the oestrus cycle, mating ability, fertility and gestation period.  

The 90-day sub-acute repeated dose toxicity study, histological evaluation of the male and female reproductive organs did not reveal any adverse effects and no changes in sperm parameters (motility and concentration) at the highest tested dose of 100mg/kg/day were detected. .

 

The results of above described key studies for reproductive/developmental toxicity have been compiled into the following matrix for overview purposes:

 

Type of study	OECD 421 (Kiss 2013)	Developmental study (Perez-D’Gregorio et al.)	Developmental study (only study with rats) (E. M. Johnson et al.)
Test sub-stance	Tellurium dioxide	Tellurium dioxide	Tellurium
Exposure period for females	14 days pre-mating, up to 14 days mating, through gestation and 4 days post-partum dosing	days 15 to 19 of gestation	days 6 to 15 of gestation
Route	oral gavage	subcutaneous	feeding study
NOAEL maternal reproductive toxicity	25 mg/kg/d	---	---
NOAEL maternal systemic toxicity	25 mg/kg/d	100 µMol/kg/d (equivalent to 31.9 mg Te dioxide/kg/d orally)	30 ppm (equivalent to 0.92 mg Te dioxide/kg/d)*
NOAEL F1	< 25 mg/kg/d (lowest dose applied)	10 µMol/kg/d (equivalent to 3.19 mg Te dioxide/kg/d orally)	300 ppm (equivalent to 8.2 mg Te dioxide/kg/d)*
Major adverse effects in off-spring	increased pup mortality in pups born alive	fetus mortality and hydrocephalus	skeletal and soft tissue malformations, primarily hydrocephali

 

*See respective comments in “Interpretation of study with respect to toxicity profile of elemental Tellurium” of above described study

 

In conclusion according to screening study Tellurium (elemental Tellurium and Tellurium dioxide) does not seem to be an overt toxicant to male rats, neither with regard to generalized systemic toxicity nor with regard to reproduction parameters (slightly reduced body weight or body weight gain at 120; no effect on reproduction parameters at 600 mg Tellurium dioxide/kg body weight per day).

 

For female rats generalized systemic and maternal toxicity has been observed, i.e. again reduced body weight and body weight gain at 120; some deaths at 600 mg Tellurium dioxide/kg body weight per day. The respective NOAELs were identical, 25 mg Tellurium dioxide/kg body weight per day.

 

Pronounced pup mortality with pups born alive was already observed at 25 mg Tellurium dioxide/kg body weight per day which is obviously a non-toxic maternal dose.

 

One developmental study [Perez-D’Gregorio et al.] revealed clear maternal toxicity at 159.5 mg Tellurium dioxide/kg body weight per day; the NOAEL being approximately 31.9 mg Tellurium dioxide/kg body weight per day (considering route to route extrapolation).

At a clearly non-toxic maternal toxic dose Tellurium caused a dramatic increase (i.e. 100 %) of hydrocephali in fetuses, i.e. the NOAEL being 3.19 mg Tellurium dioxide/kg body weight per day (considering route to route extrapolation).

 

A further developmental study with rats [ E. M. Johnson et al.] basically follows the toxicity pattern as outlined before, because maternal toxicity was observed from 300 ppm Tellurium/kg diet (equivalent to 8.2 mg Tellurium dioxide/kg body weight per day). Effects on fetuses (even though only small) were already observed at this dose and drastically increased with increasing doses with regard to the occurrence of hydrocephalus whereas maternal toxicity did not increase respectively.

 

Overall it is to be concluded that Tellurium is capable to specifically cause hydrocephali in fetuses at doses with no or only marginal toxicity to exposed dams.

 

 

Definition of starting point for DNEL derivation

Based on the findings the starting point of a DNEL derivation may be stated by the following key parameters:

 

·      (Lowest) NOAEL_subcutaneous(F1 generation) for developmental toxicity in male/female fetuses: 10 µMol/kg/d (test substance: Tellurium dioxide; developmental toxicity study with rats after subcutaneous application)

 

·      NOAEL_oral(F1 generaton) for developmental toxicity in male/female fetuses: 3.19 mg Tellurium dioxide/kg/d considering a route to route extrapolation (s.c. to oral) by factor of 2)

 

·      Observed effects: increased fetal mortality and occurrence of hydrocephalus at absence of maternal toxicity

 

In conclusion it follows that a potential starting point for the DNEL derivation with regard to developmental toxicity may be well characterized by the oral NOAEL of 3.19 mg Tellurium dioxide/kg body weight per day.

 

 

Read-across rationale for Tellurium dioxide:

Tellurium dioxide and elemental Tellurium are reduced to Telluride [Te2-] which is further metabolized to the mono- and dimethyl telluride (which are excreted to various degrees (also depended on route of exposure) in exhaled air, sweat, feces and urine) and also to the Trimethyl telluronium cation which is excreted in urine.

Since the physico-chemical behaviour of elemental Tellurium and Tellurium dioxide is the same with regard to their metabolic fate (reduction to the Telluride anion) it is highly likely that both substances will behave very similar with regard to systemic toxicity. Thus, it can be assumed that Tellurium is a suitable analogue substance to Tellurium dioxide.

This assumption is proven by a similar toxicological profile, as evidenced by the same results in various toxicological studies described below.

In acute oral toxicity studies in rats for both substances the LD50 value is > 5000 mg/kg body weight. In none of the studies an animal died.

Neither a skin nor an eye irritating property was observed in in vitro studies with both Tellurium and Tellurium dioxide.

Both substances are proven to be skin sensitizers in the Local Lymph Node Assay (LLNA).

Furthermore, negative data from bacterial reverse mutation assays (Ames–Test) for point mutations are available for Tellurium and Tellurium dioxide.

Due the common metabolic profile of the target and the source substance and the congruent results in acute and local toxicity studies, it is considered justified to address acute inhalation toxicity for Tellurium dioxide with data on Tellurium. 

In the available acute inhalation toxicity study on Tellurium, a LC50 value of > 2.42 mg/L air was determined and an Acute Tox 4 classification (H332) was derived. Even though the concentration of 2.42 mg/L is within the range of >1 ≤ 5 mg/L which triggers this classification, this hazard conclusion is clearly based on a worst-case assumption as 2.42 mg/L was the highest attainable concentration and no mortality occurred.

In general, the target substance could also have a slightly higher hazard potential due to its somewhat higher bioavailability. However, considering the clearly conservative classification made on the basis of the data on Tellurium, it is considered reasonable to assume that a possible slightly higher hazard potential of the target substance is covered by the classification. 

For developmental toxicity a very similar toxicity pattern is proven by results from the reproduction/developmental screening study with Tellurium dioxide and the developmental toxicity studies with both, source and target substance. Based on the available key data of the source and the target substance, both substances were considered to be classified as Repr. 1B; H360D.

Furthermore, the formation of identical metabolites under physiological conditions (which is described in the following) is crucial for this read-across justification.

Methylated Tellurium is identified as the central metabolite of Tellurium metabolism in mammalian cells. Since all inorganic Tellurium compounds are to be metabolized to methylated Tellurium before they are excreted into the blood stream and transported to the different (from a toxicological point of view) conceivable target organs and compartments all inorganic Tellurium compounds should be comparable with respect to their toxicological properties.

Especially effects on the unborn child as discussed for Tellurium to represent the most critical toxicological endpoint, depends on the Tellurium moiety as distributed by the blood stream.

A qualitative assessment of the hazard profile is therefore consequently not depending on the chemical species of Tellurium.

In conclusion, it is considered justified based on the practically identical metabolic fate, the similarity of physico-chemical properties, the identical toxicological profile for local and systemic endpoints, that the results from an acute inhalation toxicity study and a prenatal developmental toxicity study in rabbit conducted with Tellurium, are likely to predict the properties of the target substance Tellurium dioxide. With respect to the somewhat higher bioavailability of Tellurium dioxide, it can be assumed that a possible higher toxicological potential is covered by the conservative classifications of Acute Tox 4 (H332) based on Tellurium and the classification Repro 1B, Lact., (H360Df, H362).

Data are therefore considered as adequate to fulfil the information requirements of REACH Annex VIII, 8.5.2 (acute toxicity by inhalation) and Annex X, 8.7.2. (Pre-natal developmental toxicity) of the target substance Tellurium dioxide.

Justification for classification or non-classification

Tellurium dioxide was subject to CLH process in 2019 and 2020. The RAC in its assessment and comparison with the classification criteria concludes that tellurium fulfills the criteria for classifications as

Repr. 1B; H360 Df and Lact; H362, which was included in the 18. ATP to CLP (Regulation 2022/692 of 16 February 2022, Index-No. 052-002-00-6).

See RAC opinion CLH-O-0000006811-75-01/F adopted 11 June 2020 for detailed explanation